1. Field of the Invention
The invention relates to devices for automatically locating the position of a radio transmitter, and particularly a radio transmitter disposed in the wheel of a vehicle.
Systems for monitoring the pressure of a vehicle's tires conventionally comprise wheel units with an integral radio transmitter which regularly transmits to a central unit for processing data originating from sensors, in particular inflation pressure and temperature, as well as an identification code. The wheel units are disposed in each wheel-tire assembly of the vehicle and the central processing unit is located in the vehicle chassis. Each wheel unit has an identification code particular to it.
2. The Related Art
WO 94/20317 and U.S. Pat. No. 5,600,301 disclose a tire monitoring system. In order to function correctly, the central processing unit should have the positions of the wheel units on the vehicle with their identification codes stored in its memory. This is imperative in order to check the origin of the signals received, and thus to avoid interference with other vehicles potentially equipped in a similar manner. It is also imperative if it is to be possible to indicate the relevant tire in the case of a fault, such as, for example, a loss of pressure.
In the case of devices similar to that of the application WO 94/20317 and U.S. Pat. No. 5,600,301, this identification is carried out manually at the time when the system is first put into operation.
WO 97/06968 and U.S. Pat. No. 6,062,072 describe a device for monitoring the tires of a vehicle in which the central processing unit is connected to four receivers each disposed directly opposite one of the four wheels of the vehicle. According to the strength of the radio signal received, it is easy to determine which is the transmitter at the source of the signal received. This device, however, has the disadvantage of requiring four receivers within immediate proximity of the four wheels and of the need to connect each of these receivers electrically to the central processing unit. This makes the installation of such a system in a vehicle expensive.